1. Field of the Invention
The present invention generally relates to a multi-pin chip mounting method and apparatus based on a TAB (Tape Automated Bonding) system in which leads formed on a tape and bumps formed on an IC chip are compress-bonded after alignment thereof with each other. More particularly, the present invention relates to a TAB inner lead bonding method and apparatus capable of aligning inner leads on a tape and bumps on a pellet (IC chip) with each other with high precision even in a state in which the inner leads and the bumps overlap each other. The present invention also relates to an alignment method, a bonding tool and a bonding stage which are used in such a bonding method or apparatus, and further relates to an IC which is manufactured by use of such a bonding method or apparatus.
2. Description of the Prior Art
The TAB system is a connection method in which inner leads 2 formed on a tape 1 and bumps 3 formed on an IC chip 4 are aligned with each other and thereafter compress-bonded collectively or en bloc.
Conventionally, a wire bonding system has been widely used as a connection method for IC chips. The minimum pitch between electrodes available in the wire bonding system is about 160 .mu.m because of restriction in dimension of a bonding tool which effects thermocompression bonding of wires.
On the other hand, in IC chips such as LSI's for computers or driver IC's for liquid crystal displays having a multiplicity of input/output pins, demands for low chip cost and high packing density require the connection of 200 or more pins at a small pitch which is smaller than 160 .mu.m. The wire bonding system cannot cope with such a requirement. To contrary, in the TAB system, since the leads are connected collectively, the above-mentioned limitation imposed for the dimentional restriction of the bonding tool does not exit, which makes it possible to connect a multiplicity of pins at a very small pitch.
In a general alignment method which has hitherto been employed in the TAB system, a position of the tape 1 and a position of the IC chip 4 are individually detected and the tape 1 and the IC chip 4 are thereafter moved to predetermined positions, respectively. The prior art disclosed by JP-B-62-27735 or JP-A-58-141 employs a method in which alignment is carried out by use of an alignment mark 65 provided at any one point on the tape 1 distanced from a bonding position or a method in which a specific form of an inner lead pattern is stored and the specific pattern is detected each time a new tape is supplied, to determine the amount of deviation of the position of the tape from a predetermined position, thereby correcting the position of the tape. Also for the alignment of the IC chip 4, a pattern in the IC chip 4 having a specific form is stored and the amount of deviation of the position of the IC chip 4 from a predetermined position is determined for every IC chip 4 to correct the position of the IC chip 4.
As for the alignment of the tape 1 and the chip 4 in a direction of rotation, there has been employed a method in which a station for mechanically correcting the direction of rotation of the IC chip 4 to effect correction for the amount of rotational deviation is interposed between a tray having the IC chip 4 before bonding which is mounted thereon and a position at which bonding is to be made.
In the conventional tape bonding apparatus, an impact load imposed on the IC chip upon bonding is suppressed by lowering a bonding tool with a low air pressure applied to the tool and changing the air pressure to a high value upon start of bonding, as has been disclosed by JP-A-53-105972. The change-over of the air pressure is synchronized with a bonding start position by means of a timing cam provided in a tool driving mechanism.
In the conventional bonding tool and stage, the thermocompression bonding of leads on a tape and bumps on an IC chip is effected by use of a bonding tool having a heater. The stage having the IC chip mounted thereon has a heater just below the IC chip in order to reduce the temperature upon thermocompression bonding.
In the above-mentioned TAB system, an advanced tendency to increase of the number of pins requires more minute bumps 3 and leads 2. Therefore, alignment with much higher precision is required. However, in the above-mentioned prior art, the positions of the tape 1 and the IC chip 4 are corrected in dependence upon a mechanical precision in response to the detection of the alignment mark 65 or the like existing at a position distanced from the bonding position, and the bonding is thereafter made immediately. Thus, the accuracy or precision of alignment includes the mechanical precision in addition to the precision of detection of the alignment mark or the like. Accordingly, there is a problem that no sufficient precision of alignment is obtainable for minute leads 2 and bumps 3 for multi-pin TAB.
Also, in the above-mentioned prior art, no consideration is paid to the fact that any variation or difference in hight of bumps to which bonding is to be made exists between individual IC chips. Therefore, in the case of an IC chip having low bumps, there is a large possibility that the change-over of the air pressure to its high value occurs before the tool is brought into contact with the bumps through leads, so that an impact pressure or force is imposed on the leads and bumps by the tool. As a result, there is a problem that the concentration of stress onto the leads and/or bumps takes place so that so-called bonding damages including the breakage of leads, the peeling-off of bumps and the wallop at lower layers of bumps are liable to generate.
Further, in the collective bonding, there is an unavoidable fear that a pressure is applied to only a small number of bumps upon start of pressure application because of the presence of a difference in height between bumps in an IC chip resulting from the precision of formation of the bumps. In the above-mentioned prior art, the use of the two-level air pressure intends to cause the tool to contact many bumps at a low pressure level. However, the larger the number of leads and bumps to be bonded to each other, the lower the resistance of each bump against a pressure required during application of the pressure. Therefore, also in the collective bonding, the above-mentioned bonding damages are liable to generate.
Furthermore, in the above-mentioned prior art, no consideration is paid to the presence of fluctuation or non-uniformity of the distribution of temperatures on the IC chip, especially, between at corner portions thereof and central portions of the sides thereof to be subjected to bonding. Moreover, there is a problem that Sn or solder applied on the surfaces of the leads on the tape adheres to the bottom surface of the bonding tool to cause a one-side contact phenomenon in which only one side of the bottom surface of the tool is brought into contact with the inner leads and the IC ship, thereby making it difficult to obtain a satisfactory connection state.